Dan Wu

The Relationship between the 24 h Blood Pressure Variability and Carotid Intima-Media Thickness: A Compared Study

Large blood pressure variability (BPV) will not only harm the target organ but also increase the possibility of the cardiovascular events. Since the damage of vascular system always leads to the alteration of the carotid wall, the structure and function of the carotid artery have been extensively examined in previous studies. In this work we conduct a study (60 subjects, aged 33–79) to evaluate the relationship between BPV and carotid intima-media thickness (IMT) in Shenzhen, which is one large city in the southern area of China. In our study, the blood pressure (BP) was collected using the 24 h ambulatory BP monitoring, and the BPV was evaluated using standard deviation (SD), coefficient of variation (CV), and average real variability (ARV) during 24 h, daytime and nighttime. All the IMT measurements are collected by ultrasound. The results show that both the daytime, and 24 h systolic BPV evaluated by three indices are positively associated with IMT. Among them, daytime systolic BPV evaluated with ARV is the best variable to represent the increasing of carotid IMT. In addition, after adjusting by age, sex, smoking, hypertension, and mean BP and PP values, 24 h diastolic BPV evaluated with SD also presents the favorable performance.

Comparison of Heart Rate Variability from PPG with That from ECG

Because it is more convenient to measure photoplethysmography (PPG) than ECG, PPG is supposed as a surrogate of ECG for heart rate variability (HRV) analysis. In this study, we measured the spectrum of pulse rate variability (PRV) from PPG and its square coherence spectrum with HRV from ECG before and after exercise. The results showed that the spectrum of PRV corresponds almost well with HRV, especially for the healthy subjects at rest. However, stimuli conditions such as exercise will decrease the correlation, especially for the high frequency (HF) component. It indicates that whether PRV can be used as an alternative to HRV depends on the applications and conditions.

A stochastic filtering approach to recover strain images from quasi-static ultrasound elastography

BackgroundModel-based reconstruction algorithms have shown potentials over conventional strain-based methods in quasi-static elastographic image by using realistic finite element (FE) or bio-mechanical model constraints. However, it is still difficult to properly handle the discrepancies between the model constraint and ultrasound data, and the measurement noise.MethodsIn this paper, we explore the usage of Kalman filtering algorithm for the estimation of strain imaging in quasi-static ultrasound elastography. The proposed strategy formulates the displacement distribution through biomechanical models, and the ultrasound-derived measurements through observation equations. Through this filtering strategy, the discrepancies are quantitatively modelled as one Gaussian white noise, and the measurement noise of ultrasound data is modelled as another independent Gaussian white noise. The optimal estimation of kinematic functions, i.e. the full displacement and velocity field, are computed through this Kalman filter. Then the strain images can be easily calculated from the estimated displacement field.ResultsThe accuracy and robustness of our proposed framework is first evaluated in synthetic data in controlled conditions, and the performance of this framework is then evaluated in the real data collected from elastography phantoms and patients with favourable results.ConclusionsThe potential of our algorithm is to provide the distribution of mechanically meaningful strain under a proper biomechanical model constraint. We address the model-data discrepancy and measurement noise by introducing process noise and measurement noise in our framework, and then the mechanically meaningful strain is estimated through the Kalman filter in the minimum mean square error (MMSE) sense.

Influence of blood pressure variability on early carotid atherosclerosis in hypertension with and without diabetes

AbstractCarotid intima-media thickness (IMT) has been one widely used index of early carotid atherosclerosis. We speculated that the influence of blood pressure variability (BPV) on early carotid atherosclerosis may be varied by the location of the carotid artery and diabetes history. Thus, the goal of this study was to evaluate the effects of BPV on early arteriosclerosis progression in different segments of the carotid artery for hypertension with and without diabetes.A total of 148 hypertension patients who underwent 24 hours ambulatory blood pressure (BP) monitoring and carotid ultrasonography were enrolled in this study. Of them, 84 subjects were without diabetes, and 64 subjects were with diabetes. Short-term BPV during daytime, nighttime, and over 24 hours were evaluated through standard deviation (SD) and average real variability (ARV). We measured carotid IMT at left and right common carotid artery (CCA), carotid bulb, and the origin of the internal carotid artery (ICA). The associations between segment-specific measurements of carotid IMT and 24 hours ambulatory BPV were analyzed.We found that IMT at the common carotid artery (CCA-IMT) and IMT at the internal carotid artery (ICA-IMT) were more closely associated with BPV than was carotid bulb IMT. In addition, for all subjects, BPV was clearly associated with left CCA-IMT but not with right CCA-IMT. Furthermore, in diabetes patients, nighttime systolic BPV was independently related to mean CCA-IMT (P < 0.01) and mean bulb IMT (P < 0.01). In contrast, in nondiabetes patients, daytime and 24 hours systolic BPV was positively associated with mean CCA-IMT (P < 0.05), but not independent after adjusting for baseline characteristics such as age and sex.The findings of our study indicate a segment-specific association between carotid IMT and 24 hours ambulatory BPV, and the associations also vary according to the diabetes history. We conclude that BPV plays a distinct role in early carotid arteriosclerosis progression within different segments of the carotid artery, especially for the hypertensions with and without diabetes.

Influence of beat-to-beat blood pressure variability on vascular elasticity in hypertensive population

Whether elevated beat-to-beat blood pressure variability (BPV) has an influence on vascular elasticity is confounded and poorly understood. This study hypothesized that the increased BPV could have an adverse effect on the vascular elasticity, as estimated by total arterial compliance (TAC), independent of blood pressure (BP) values. Beat-to-beat BP and TAC were measured in 81 hypertensive patients (experimental population) and in 80 normal adults (control population). Beat-to-beat BPV was assessed by standard deviation (SD), average real variability (ARV), residual standard deviation (RSD) and variation independent of mean (VIM). In experimental population, systolic BPV (SBPV) showed a significant correlation with TAC (SD, r = −0.326, p < 0.001; ARV, r = −0.277, p = 0.003; RSD, r = −0.382, p < 0.001; VIM, r = −0.274, p = 0.003); similarly, SD, RSD and VIM of diastolic BP (DBP) also showed explicit correlation with TAC (r = −0.255, p = 0.006; r = −0.289, p = 0.002; r = −0.219, p = 0.019; respectively). However, in the control population, neither SBPV nor diastolic BPV (DBPV) showed a significant correlation with TAC. Furthermore, in the experimental population, VIM of systolic BP (SBP) was also a determinant of TAC (β = −0.100, p = 0.040) independent of average SBP, DBP, age and body mass index. In conclusion, these data imply that beat-to-beat BPV, especially SBPV, shows an independent correlation with vascular elasticity in hypertensive population.

Association between beat-to-beat blood pressure variability and vascular elasticity in normal young adults during the cold pressor test

Abstract The beat-to-beat blood pressure (BP) monitoring parameters, such as average beat-to-beat BP, BP variability (BPV), could have an influence on the vascular elasticity. This study hypothesized that the elevated beat-to-beat BPV could evoke the reduction of the vascular elasticity independent of BP levels. We measured the beat-to-beat BP recordings and total arterial compliance (TAC), which was used to assess the vascular elasticity, in 80 young healthy adults during the cold pressor test (CPT). The CPT included 3 phases: baseline phase, cold stimulus phase, recovery phase. Six parameters were used to estimate BPV. In bivariate correlation analysis, TAC showed a significant correlation with systolic BP (SBP) and diastolic BP (DBP) in the cold stimulus phase; and 4 indices of SBP variability (SBPV) were associated with TAC (r = 0.271∼0.331, P ⩽ 0.015) in the recovery phase; similarly, 2 indices of DBP variability (DBPV) were also correlated with TAC (r = 0.221∼0.285, P ⩽ 0.048) in the recovery phase. In multivariate regression analysis, DBPV (&bgr; = 0.229, P = 0.001) was a determinant of TAC independent of average DBP, sex, and weight. In addition, both beat-to-beat BP and BPV values increased in the cold stimulus phase (P < 0.01); whereas, the TAC decreased in the cold stimulus phase (P < 0.01). In conclusion, these data suggest that the beat-to-beat DBPV shows an independent association with the vascular elasticity in young normal adults during the CPT.

Analysis of beat-to-beat blood pressure variability response to the cold pressor test in the offspring of hypertensive and normotensive parents

Abnormal autonomic nervous regulation has an important role in the development of hypertension. As to whether blood pressure (BP) or BP variability represents the proper characteristics for predisposition to hypertension in Chinese young adults remains controversial. We studied the properties of the indices extracted from beat-to-beat BP during a 13 min cold pressor test (CPT). In this study, 69 Chinese young adults including 34 offspring of hypertensive parents (OHPs; 25.6±2.5 years) and 35 offspring of normotensive parents (ONPs; 25.3±2.3 years) were analyzed. We assessed the differences between the two groups regarding mean beat-to-beat BP and variability indices. Beat-to-beat BP variability indices included time-domain indices and frequency-domain indices. Our results showed that the differences in beat-to-beat systolic BP and mean BP levels between the OHPs and the ONPs were statistically significant (P<0.05). Furthermore, more BP variability indices in the frequency domain were significantly different between the two groups. We concluded that BP variability was superior to BP as an index to evaluate the cardiovascular and sympathetic reactivity to the CPT. Moreover, compared with time-domain BP variability, we found more differences in frequency-domain BP variability between the two groups, thus indicating that frequency-domain BP variability may be a potential index of predisposition to hypertension.

AN ACCURATE CALIBRATION METHOD FOR THE MEASUREMENT OF ARTERIAL OXYGEN SATURATION USING PHOTOPLETHYSMOGRAPHY

The monitoring of arterial oxygen saturation (SaO2) is a common practice in both clinical and home environments, and the process of monitoring can be exercised invasively or non-invasively. In the past decades, the pulse oximeter is one of the most popular non-invasive devices that use photoplethysmography (PPG) to measure SaO2. As the pulse oximeter requires calibration prior to application in clinical practice, a significant number of calibration methods have been proposed based on experimental data collected from human volunteers. Alternatively, models may be derived from the Lambert–Beer law or the photon diffusion equation (PDE). However, most of such calibrated oximeter can only provide accurate readings of SaO2 at high versus the low levels. We propose to apply an extra-boundary condition to solve the PDE, and then to develop a model-based calibration method that relate optical measurements to the level of SaO2 in this work. Then, we validate our method against previous model-based methods and an oximeter simulator with higher accuracy when the level of SaO2 is greater than 90%. In practice, our model-based method can still maintain a good performance when the level of SaO2 decreases to 60%, thereby demonstrating high potential in the accurate evaluation of the oxygen level of patients by PPG.

The relationship between heart-carotid pulse transit time and carotid intima-media thickness in hypertensive patients

The study aimed to investigate the relationship between heart-carotid pulse transit time and carotid intima-media thickness (CIMT) in hypertensive patients, and whether including the pre-ejection period (PEP) in heart-carotid pulse transit time would affect this correlation. A total of 62 hypertensive patients were included in this study. They were divided into the normal CIMT group (n=33, CIMT⩽0.8 mm) and the thickened CIMT group (n=29, CIMT>0.8 mm). The noninvasive ultrasound method was used to measure CIMT, electrocardiogram R-wave-based heart-carotid pulse transit time (rcPTT) and PEP. Aortic valve-carotid artery pulse transit time (acPTT) was calculated by subtracting PEP from rcPTT. Simple linear analysis showed that CIMT was negatively associated with rcPTT and acPTT (r=−0.57, P<0.0001; r=−0.41, P=0.016) in the normal CIMT group as well as in the thickened CIMT group (r=−0.50, P=0.0053; r=−0.59, P=0.001). These relationships were eliminated in the normal CIMT group after adjusting for age, gender, smoking behaviour, systolic blood pressure, diastolic blood pressure and cholesterol levels. However, rcPTT and acPTT still showed significant correlations with CIMT in the thickened CIMT group. In conclusion, rcPTT and acPTT were associated with CIMT, independent of well-known clinical confounders in thickened CIMT hypertensive patients. Therefore, rcPTT and acPTT might be useful markers for atherosclerosis evaluation.

Motion Estimation of Common Carotid Artery Wall Using a H ∞ Filter Based Block Matching Method

The movement of the common carotid artery (CCA) vessel wall has been well accepted as one important indicator of atherosclerosis, but it is still one challenge to estimate the motion of vessel wall from ultrasound images. In this paper, a robust H ∞ filter was incorporated with block matching (BM) method to estimate the motion of carotid arterial wall. The performance of our method was compared with the standard BM method, Kalman filter, and manual traced method respectively on carotid artery ultrasound images from 50 subjects. Our results showed that the proposed method has a small estimation error (96 μm for the longitudinal motion and 46 μm for the radial motion), and good agreement (94.03% results fall within 95% confidence interval for the longitudinal motion and 95.53% for the radial motion) with the manual traced method. These results demonstrated the effectiveness of our method in the motion estimation of carotid wall in ultrasound images.